Added configurable offsets to the per-packet overhead in ANA.

modules/audio_coding/audio_network_adaptor/include/audio_network_adaptor_config.h

 /*
  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 14 matching lines @@
   // Note: This is what we tell the encoder. It doesn't have to reflect
   // the actual NetworkMetrics; it's subject to our decision.
   rtc::Optional<float> uplink_packet_loss_fraction;
   rtc::Optional<bool> enable_fec;
   rtc::Optional<bool> enable_dtx;
 
   // Some encoders can encode fewer channels than the actual input to make
   // better use of the bandwidth. |num_channels| sets the number of channels
   // to encode.
   rtc::Optional<size_t> num_channels;
+
+  // This is true if the last frame length change was an increase, and otherwise
+  // false.
+  // The value of this boolean is used to apply a different offset to the
+  // per-packet overhead that is reported by the BWE. The exact offset value
+  // is most important right after a frame length change, because the frame
+  // length change affects the overhead. In the steady state, the exact value is
+  // not important because the BWE will compensate.
+  bool last_fl_change_increase = false;
 };
 
 }  // namespace webrtc
 
 #endif  // MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_INCLUDE_AUDIO_NETWORK_ADAPTOR_CONFIG_H_